Well Jeff it might be trapped air in the bow I'm not that sure. We were on a schedule yesterday and I only had an hour there to play.

She dives stern first. Once under she's fine but it was quite shallow at this end of the lake. Until I have tested her more it's the safest place to be.

Here's some video which will show you what I mean. She need bigger rudders for sure and I plan to make slip on so they can be removed for display. She had plenty of head speed bu needs to sit lower in the water to keep the prop from cavitation.

That just requires a bit more water in the tank to lower the free board for runs and back up full at the dock.

Diving stern first can be due to the ballast tank being situated too far aft. But it can also be the result of hydrodynamic flow around the bow causing lift. My Seehund does this quite noticeably. I counter this by applying down force on the stern planes. I should note that the Seehund dives perfectly level when not moving.

Watching the video, it wasn't clear if the boat would hold a level trim when not moving and just part of the conning tower out of the water? (and the air vented from the bow of course!)

It does look like at least part of the trim issue will be solved by adding more ballast up front.

All good and accurate observations Jeff. Bob was a bit concerned that the tank was too far forward of the CG of the boat. It is at optimum with the space and shape of the hull the Cylinder can not be moved any further back or forward.

Looking at the video again and again I do believe it is trapped air I need to better vent. It holds pretty darn level under water but I kept hitting the shallow bottom.

And to be completely honest I just didn't think about applying any down at all in the dive. Just didn't occur to me but next time. I may have to increase the throws on the dive planes as it is I had them set pretty low.

First time runs are always a learning experience. One more ought to get the bugs out.

I knew those rudders wouldn't be enough. Double the area, then it will turn.

Surprised you're getting trapped air on this boat, you have a lot of large holes drilled at bow, so the air should get out easily.Running a countersink bit underneath the holes would help ventilation if you haven't done that already.

Had a look at some of the earlier stills. There is what looks like a valve, or some kind of access point near the tip of the bow that I've circled in red. Can this be opened up? If so that should eliminate any trapped wind problems (I'd still countersink the underside of the other holes).

I made this for Bob. Thought I'd share it her. His wife Liz informed me today Bob will be in hospital for a week or so. Not sure what for but send him and email and tell him we wish him well and a speedy recovery!